IE881584L

IE881584L - Hitch control system with start-up lock-out

Info

Publication number: IE881584L
Application number: IE881584A
Authority: IE
Inventors: Thomas Eugene Boe; Richard Langel Sweet
Original assignee: Deere & Co
Priority date: 1987-05-27
Filing date: 1988-05-26
Publication date: 1988-11-27
Also published as: DE3867533D1; ATE71245T1; AU596894B2; EP0292859B1; DK292688D0; CA1308464C; ES2028174T3; JPH0829003B2; AU613826B2; AU4979190A; AU612072B2; JPS63309102A; ZA883773B; AU1664488A; AU4979090A; IE61535B1; US4837691A; EP0292859A1; DK292688A; MX168242B

Abstract

A hitch control system includes an algorithm which prevents undesired and/or unexpected hitch movement upon start-up of the control system, depending upon the actual hitch position, the commanded hitch position and an operator set limit position.

Description

1 0 15 20 25 30 35 4 0 45 50 61 535 2 This invention relates to a method and a device for controlling the position of a hitch appliance of a vehicle, to which a ground-working implement can be attached. The control system derives a command value, a measured position value and if required a limit value signal. The command value corresponds to a desired control characteristic of the hitch appliance and is adjustable by a control device. The measured position value gives the actual position of the hitch appliance and is determined by a position sensor. The limit value signal corresponds to a desired limit position of the hitch appliance and is generated by a manually adjustable limit value setter. The control system generates control signals automatically in dependence on the command value andthe measured position value, inaccordance with whichthe hitch appliance is raised and lowered within a positional range. The control system comprises a device which prevents inadvertent movements on starting up the control system. Such a control system is known from Patent Specification No. 313/85.

To adjust the working depth of an implement attached to a tractor, control systems are used which control the working depth of the implement on the basis of various measured and operator-determined parameters. The present invention concerns especially the starting up operation of such a control system.

Even when an electro-hydraulic control system for a hitch appliance is turned off the control elements can by manually adjusted. However there is then no corresponding movement of the hitch appliance effected by the control system. Such an adjustment can lead to unexpected movement of the hitch appliance as soon as the system is turned on again.

In Patent Specification No. 313/85 there is described a control system for a hitch appliance. This system includes a starting action in which the inadvertent movement of the hitch appliance after turning on the control system is prevented until the control elements have been adjusted to a position which corresponds to the actual position of the hitch appliance. Another control system for hitch appliances is described in US-PS 4 518 044. This system controls the hitch appliance of the tractor in dependence on measured and predetermined draft forces, measured and predetermined positions of the hitch appliance, measured engine speed and measured wheel slip. It is desirable also in such a system to provide a start-up interlock which prevents inadvertent movement of the hitch appliance during the starling operation of the control system, so long as certain conditions are not satisfied.

The object of the invention is to develop further a control system according to Patent Specification No. 313/85.

This-problem is solved according to the invention in that a hitch appliance control system, which can be based on a microprocessor, includes a start-up interlock algorithm which prevents undesirable and/or unexpected draft movements directly after the turning on of the control system.

In particular a method is proposed which, in the case when the actual position of the hitch appliance lies outside the limit position on starting up of the control system, the control system prevents movements of the hitch appliance until, as a result of manual adjustment of the control device the corresponding position of the hitch appliance has reached the limit position and/or until, as a result of a manual adjustment of the limit value setter the limit value signal corresponds to the actual position of the hitch appliance.

The method can also be amplified or modified to the effect that, on starting up the control system, this compares the position of the control device with its limit position and prevents movement of the hitch appliance so long as the position of the control device deviates from the limit position.

An advantageous development of this method is seen in that, when the control device has been moved from a central position to the limit position, the control signal so affects the hitch appliance that this is moved to a position which corresponds to the limit position of the control device.

The problem is also solved according to the invention by a control system of the kind initially referred to. which is characterized in that the start-up interlock device comprises a 3 comparator device for determining whether the actual position of the hitch appliance lies outside the limit position, and includes a discriminatorwhich causes the provision of a control signal by means of which the actual position of the hitch appliance is maintained and movement of the hitch appliance is prevented, until the command value reaches a value corresponding 5 to the limit position as a result of a manual adjustment of the control device and/or until the limit value signal reaches a value corresponding to the position of the hitch appliance as a result of a manual adjustment of the limit value setter.

An advantageous modification or development of this control system is seen in that the start-up interlock device comprises a comparator device for determining the position of the 10 control device relative to its limit position and includes a discriminator which provides a control signal, through which the actual position of the hitch appliance is maintained and movement of the hitch appliance is prevented so long as the position of the control device deviates from the limit position.

This control system can be developed in advantageous manner in that the start-up , 15 interlock device includes a monitoring device which tests whether the control device has been moved from a central position to the limii position and, only When this occurs, causes the provision of control signals which move the hitch appliance to a position corresponding to the limit position.

By means of the invention undesired and/or unexpected movements of the hitch 20 appliance during the turning on of the control system of the hitch appliance are prevented. In particular a start-up interlock algorithm in correspondence with the invention prevents movements of the hitch appliance during start-up of the control system which result from an alteration in the position of the hitch appliance or an alteration in the position of the control I ever, which have occurred while the control system was not in operation. This algorithm 25 prevents not only movements as a result of an erroneous relationship between the position of the control lever and that of the hitch appliance but it also minimises movements which can be caused by valve leakage. The unlocking of the hitch appliance is achieved in that the control signal for the hitch appliance is so changed that it passes through the value of the position measurement signal of the hitch appliance, which was reached on turning on, or in that the 30 control lever for adjusting the position of the hitch appliance is moved to one of the two end positions, whereby a movement of the hitch appliance to the end position is permitted. When the control lever is at one of the two end positions in turning on the control system, the lever must be moved away from the end position and then back again, in order to effect a movement of the hitch appliance. 35 This turn-on interlock algorithm also prevents a movement of the hitch appliance which could be caused by a change of the upper limit value during a turned off phase. Should the position of the hitch appliance on turning on be above the upper limit value, action on the hitch appliance through the upper limit value is prevented until the ope'rator has moved the hitch appliance below the upper limit value or until the operator has adjusted the upper limit value 40 above the position value of the hitch appliance. Accordingly movements of the hitch appliance are prevented from occurring on turning on when the position of the hitch appliance on turning on of the control system is located outside limit values which have been adjusted by an operator or when the manual control parameters have been altered during a turned off phase.

The control system for the hitch appliance can also include switches which are fitted 45 outside the tractor cab, so that an operator can also raise and lower the hitch appliance from there. The present turn-on interlock algorithm is not affected by the actuation of such switches.

Furtheradvantageousdevelopmentsandadvantagesaredescribedandexplainedwith reference to an embodiment, which is represented in the drawings. These show: 50 Figure 1 a simple representation of an agricultural tractor, which is provided with the present invention.

Figs. 2a - 2f a flow diagram of the algorithm which is implemented by a central control unit and Figure 3 a detailed view of the control lever. 55 Figure 1 shows a tractor 10, whose rear frame 20 supports a rear axle 22 and a lift shaft 24. An implement hitch appliance 26, for example a conventional three-point hitch ■4 appliance, comprises lower links 28. which are connected to lift arms 30 through lift rods 32. The lift arms 30 are connected to the lift shaft 24, in order to ensure simultaneous and like movements. They are raised and lowered by a pair of parallel, fixed hydraulic drives or lift shaft cylinders 34. A drawbar 36 extends out behind the housing 20. The tractor 10 and the hitch 5 appliance 26 are only presented by way of example. The invention can also be employed with tractors and hitch appliances of different configuration. The invention can also be used in a tractor with articulated four-wheel drive or a front-wheel drive wide track tractor, for example.

A ground-working implement (not shown) adapted to be built on, such as e.g. a share plough or a chisel plough, can be attached in normal mannerto the lower links 28. Alternatively 10 a towed implement (not shown) can be connected to the drawbar 35. In the hitch appliance, e.g. in the lower links 28, there can be built draft load sensors 38, in order to measure the draft forces which are transmitted to the lower links 28 from the coupled, implement. If the attachment appliance 26 includes a plurality of draft load sensors 38, a single draft load signal representing the draft force can be formed in that the individual signals of the sensors 38 are 1 o combined. In the case of a towed implement, the draft forces can be measured by a draft load sensor which is-fitted into the drawbar 36 or into erupting foch^rmeeied to the-lower links 28. In both cases any suitable known draft load sensor can be used.

The hydraulic fluid flow to and from the lift shaft cylinder 34 or to and from a remote cylinder, not shown, of a towed or half-integrated attached implement, is controlled by a 20 customary magnetically controlled, electro-hydraulic flow control valve 42, the electrical control signals for which are generated by a control device or a central control unit 50, where the latter can include a digital microprocessor, an analog/digital converter, multiplexer and/or other normal hardware parts. The flow control valve 42 can be a servo-valve of MOOG type usual in the art with a control stage controlled from a torque motor and an integrated 25 secondary stage. The flow velocity of the hydraulic medium is substantially proportional to the magnitude of the electric current which drives the torque motor of the valve 42.

An adjustable position/draft load control lever 52 is connected to a lever setting transducer 54 (for example a potentiometer), which generates a command value which, for its part, corresponds to a desired position of the hitch appliance 26 or a desired draft load, 30 depending on the setting of position/draft load mode switch 56. An electrical upper limit signal is obtained from a manually adjustable potentiometer 51. The lever 52 moves within a slot 57. The end points 53 and 55 of this slot 57 act as mechanical upper and lower stops, which limit the position of the control lever 52 mechanically, whereby the signals of the potentiometer 54 are also limited. 35 A position measuring device SO, for example an ordinary rotary potentiometer, generates a position signal which corresponds to the measured position of the lift shaft 24. A position feedback signal can also be derived from the lift shaft cylinder 34 or a remote lift cylinder, when this cylinder has a position transducer, as is described in US-PS 3 726 191 for example. 40 The above-described hardware elements as well as the algorithm features described below can be combined with other control elements forthe hitch appliance, as is described in US-PS 4 518 044.

Furthermore a raise and a lower switch 70,72 can be arranged outside the tractor cab in the vicinity of the hitch appliance, which makes it possible for an operatorto raise and lower 45 the hitch appliance 23 also from a location which lies outside the tractor cab.

The control algorithm which underlies the method or the control system according to the invention is shown in Figures 2a to 2f. The algorithm begins at step 100, after which various variables as follows are initialised and set to '"false": UNLOCK means that the hitch appliance 26 is unlocked, 50 LOWVER 1 means thai the control command forthe hitch appliance 28 has bean lowered since the turning on of the control unit 50, RAISE 1 means that the control command for the hitch appliance 26 has been raised since the turning on of the control unit 50, 5 LOKTOP means that the upper limit value of the hitch appliance 25 is unlocked, LOKSAV means that the position of the hitch appliance 25 which it occupied on turning on the control unit 50 has been saved, SLEW means that a change in the position of the hitch appliance 25 is allowed. 5 In step 104 the input values of the hitch appliance control are read and so normalised that all inputs lie between 0 and 255. The significant input values for the start-up interlock algorithm are as follows: FDBK feedback signal of the position of the hitch appliance 25, LEVER setting of the control lever 52, 10 COMMAND control command of the position control;-which is-determined t>y the control lever 52, TOP control signal forthe upper limit value of the hitch appliance 25 in accordance with the limit value setter 51.

In steps 10S to 110 it is ascertained whether the position (FDBK) of the hitch appliance 15 25 on starting the control unit 50 must be saved. If necessary it is saved in FDBKLC. This is effected in that it is checked whether the hitch appliance 25 is unlocked and whether the position of the hitch appliance 26 has been saved. Test 105 checks the state of the UNLOCK flag bit, in order to determine if the hitch appliance 25 is unlocked and step 108 checks the state of the LOKSAV flag bit in order to determine whether the position of the hitch appliance 20 has been saved. Should both be false, step 110 gets the position of the hitch appliance(FDBK) on turning on the control unit 50 into the register FDBKLC.

Steps 112 to 122 check the upper limit value of the hitch appliance 25 (TOP), in order to determine whether it is to be used as control limit value (unlocked). For this it is determined whether the hitch appliance 26 has a position below the upper limit value. If this is so, the 25 upper limit value is unlocked. Step 112 checks whether the upper limit value, which is set by the potentiometer 51, is lower than the position of the hitch appliance (FDBK) and branches the test to step 11S should this be so, or to step 114 if not. If the upper limit value lies above the position of the hitch appliance 26, the control command (COMMAND) for the hitch appliance 23 is limited by steps 120 and 122 to the upper limit value (TOP). If the lever is 30 unlocked (UNLOCK® true, step 114), then the upper limit value is likewise unlocked (TOPLOC == true, step 118), before the control command is limited in steps 1 20 and 122. If the hitch appliance 2S lies above the upper limit value, the control command is only limited (steps 120 and 1 22) when the upper limit value is unlocked (LOKTOP M true, step 113).

The steps 124 and 123 unlock the hitch appliance 23 whenever the external switches 35 70, 72 are operated.

The steps 128 to 144 and 146 move the hitch appliance 23 to the position which is determined by the lever 52 as soon as the lever 52 is adjusted to one of the two end positions. This occurs in that it is checked whether the lever has ever been moved from the end positions 53.55 (SLEW® true). Then the start position of the hitch appliance 23 (FDBKLC) is increased 40 (or reduced) if the lever is at an end position.

Step 128 determines which of the two end positions 53,55 lies nearertothe lever 52. If the lever 52 is nearer to the upper end position 55 (LEVER > 128), the program branches to step 132. If not, it branches to step 130. In the steps 130 and 132 the program determines if the lever is at least 1.5% from the end position (LEVER > 4 at the lower end or LEVER <251 45 at the upper end). If the lever is not located in the neighbourhood of an end position, this is stored in step 134 (SLEW - true) and the program proceeds with step 148. If the lever 52 is located in the neighbourhood of an end position 53. 55, it is checked in steps 136 and 138 whether it is actually at an end position 53, 55. Ifthe lever is not actually at one of the two end positions 53, 55, the program proceeds with step 148. If however the 52 is at one of the two ©r end positions 53, 55, it is checked in step 140 or 142 whether the lever 52 was previously removed from the end position 53, 55 (SLEW = true). When this applies, the starting position (FDBKLC) is increased stepwise (step 46) or lowered (step 144). The algorithm then proceeds with step 148. This causes a stepwise movement of the hitch appliance 26 to a position which 5 corresponds to the corresponding end position 53 or 55 of the lever 52. If SLEW is not true, the program proceeds without altering the start position of the hitch appliance 23. In step 148 the valve control signal which is necessary to hold the hitch in the start position, is computed in accordance with the following equation: HPERR - [(FDBKLC - FDBK) x 256 x G1 8] / 128 + G19 10 where G18 is a constant which represents the amplification factor of the valve (the value can lie between 26 and 55)andG19 is a constant which represents the response threshold of the valve (typical value about 1250). This is in principle the same equation as is used in the normal position control for hitch appliances, with the difference that FDBKLC is fed in instead of the control signal of a control lever. In step 150 the set-point command (HVCOHer #>e- control 15 valve of the hitch appliance 26 is computed. This step represents a control algorithm for the hitch appliance 26 as is described in US-PS 4 518 044.

Steps 1 52 to 162 determine whether the hitch appliance 26 can be unlocked. The hitch appliance 26 is unlocked if the set-point command forthe valve of the hitch appliance 26 (HVCO) of step 1 50 is equal to 0 or has passed through the zero value since start-up. Step 20 152 examines whether the valve control command is 0 (HVCO = 0) and unlocks the hitch appliance (UNLOCK - true, step 162) should this be so. Step 1 54 tests the direction of the control command for the hitch appliance 26 (HVCO > 0?) and indicates that a command to raise the hitch appliance 26 has been given (RAISE! *= true, step 158) if an actuation of the pressure valve is necessary, or that a command to lowerthe hitch appliance 26 has been given 25 (LOWER 1 ■ true, step 1 56) if an actuation of the return valve is necessary. Step 160 then checks whether lowering and also raising commands have been given since turning on and unlocks the hitch appliance 26 if this is so (UNLOCK = true, step 162).

Step 164 determines the valve command for control of the hitch appliance 26. If the hitch appliance is unlocked (UNLOCK = true), the program proceeds to step 168 and passes 30 on the set-point value (HVCO) forthe valve for control of the hitch appliance from step 150 to the corresponding valve. If the hitch appliance 26 is not unlocked, the program goes to step 166 and gives the necessary valve eontrol command to the valve in order to hold the hitch appliance 26 in its start-up position (HPERR) according to step 148.

From here the program returns to step 104 in order to receive new data. The loop of 35 steps 104 to 166 or 168 is executed so long as the control system for the hitch appliance 26 is in operation.

The conversion of the above-described flow diagram into a programming language, so that the algorithm, as described in the flow diagram, can be applied in a digital data processor, e.g. a microprocessor, presents no problem to those skilled in this art. 40 Althoughtheinventionhasbeendescribedinconjunctionwithaparticularembodifnent, it is apparent in the light of the preceding description that many alternatives, changes and variations are obvious to those in the art. ?